The present invention concerns a window assembly and method for producing same and, in particular, a method for producing curved window assemblies which are electrically heated.
Motor vehicles of recent manufacture are equipped with various systems for defogging and deicing the windows. Generally, the windshield has warm air blown across its interior which is generated by the use of heat transferred from the internal combustion engine driving the vehicle to the engine cooling system and further to air circulated by the vehicle ventilation system. In such a case, there is a period of time between the starting of the engine and the time that sufficient heat is being generated in the cooling system in order to provide the defogging and deicing warm air. Depending upon the temperature conditions and the time the vehicle has been sitting idle without its engine running, the period of time before sufficient heat is available to accomplish the desired function can be significant.
An alternative system generates heat from electrical energy obtained from the vehicle electrical system. Many different systems have been proposed for electrical heating including the placement of an electrically conductive transparent coating on the windshield and embedding fine wires in a laminating interlayer of the windshield. However, such a system is expensive to manufacture due to vision requirements including the desire to reduce reflections. In addition, the fine wires and conducting films utilized are difficult to install and are subject to circuit interruption due to thermal and mechanical stresses.
U.S. Pat. No. 2,954,454 discloses an electrically conducting curved glass windshield and a method of producing the same. A flat sheet of glass has strips of fusible material applied thereto in spaced areas and preferably along the opposed margins of the sheet in substantially parallel relation. The glass sheet is heated substantially to its point of softening and simultaneously the fusible material is fused to the glass to form electrodes or bus bars. The surface of the heated glass sheet is sprayed with a suitable material, such a a tin halide, to form upon the sheet a transparent, continuous though extremely thin electrically conducting coating of tin oxide. The glass sheet is cooled in air at room temperature and the electrodes are connected to suitable leads which in turn will be connected to the vehicle electrical system. The glass sheets are paired with a second glass blank on a bending mold and heated such that the glass settles into the desired windshield shape. The glass is slowly cooled and cut to the desired shape.
U.S. Pat. No. 3,001,901 discloses a method of producing electrically conductive articles such as a transparent electrically conductive film on a plastic sheet. A sealer coating is placed on the sheet while it is in a flat form. An adhesive layer formed of a metal oxide is placed in contact with the sealer coating and a transparent electrically conductive film is deposited on the adhesive layer. The composite structure is heated to an elevated temperature above the normal temperature to which the sheet will be heated by the electrically conductive film. At the elevated temperature, electrodes are placed in contact with the conductive film and the article is allowed to cool to place the electrodes in compression. In the heated state, the sheet can be bent and/or laminated to another plastic sheet to produce an assembly.
U.S. Pat. No. 4,373,130 discloses a windshield having an electric resistance heating element located in a lower region normally outside the driver's field of vision where at least one windshield wiper is located in the rest position of the wiper. A continuous layer of a heat radiation absorbing ceramic material opaque to ambient light and coextensive with the area of the heating element is disposed on the windshield between the heating element and the windshield wiper to shield the heating element from view from the front of the windshield and to uniformly distribute heat over the lower portion of the windshield. The windshield is manufactured by applying a continuous closed layer of a printable baking paste to the surface of a glass pane by a screen printing process. The layer is dried and imprinted with an electric heating resistance material. The electric heating resistance material is dried and an additional continuous closed layer of a printable baking paste can be printed on the electric heating resistance material. The baking is done in a single heat treating process. In a laminated windshield, the first layer and the electric heating resistance material are applied to the inner surface of the outer pane. The second layer of printable paste is applied to the outside surface of the inner glass pane. After all the layers have been applied and dried, the two glass panes are placed together and subjected to joint bending with heating.
U.S. Pat. No. 4,407,847 discloses a process for manufacturing electrically heated backlites. An opaque band is applied to the surface of a glass sheet with a radiation curable paste that includes both a filler material which can fuse to the surface of the glass when heated to a fusion temperature and radiation curable material which is heat decomposable into complements which are non-reactive with the glass sheet when heated to a fusion temperature. The radiation curable material is cured to temporarily bond the radiation curable paste to the glass sheet. A pattern of electrically conductive material is deposited on the surface of the glass sheet and contains at least one component which is heat fusible with the surface of the glass sheet when the glass sheet is heated to the fusion temperature. The glass sheet is passed through a heating lehr which is operated at a temperature sufficiently high to heat the glass sheet to the fusion temperature.
One material commonly used for bus bars is silver. However, one problem encountered with the use of silver material for a bus bar is bleed-through of the silver through a ceramic enamel band utilized to hide the bus bars. Such a condition is visually unacceptable to vehicle manufacturers.